Conventionally, there is a processing unit in which a developing unit (a unit having a toner cartridge) is integrated with a photoconductive drum and which is detachable from a main body of an image forming apparatus so that a user can exchange the developing unit and the photoconductive drum without the help of a serviceman (Japanese Unexamined Patent Application Publication No. Hei 8-16072 and Japanese Unexamined Patent Application Publication No. 2005-275341). The image forming apparatuses provided with a processing unit include an image forming apparatus which, for the sake of the operation of a user when exchanging the processing unit, has an opening for inserting and detaching a processing unit on the front wall thereof.